In 1996, in a rare display of bipartisanship and without a single dissenting vote, US Congress passed the Food Quality Protection Act, ordering the Environmental Protection Agency to review nearly 500 pesticides and ban or restrict those that posed hazards to human health. Then the real fight began translating a broad mandate into specific regulations that were almost certain to displease somebody. Last week, Carol Browner, the E.P.A. administrator, fired her first shot, announcing tough new restrictions on two widely used pesticides. But it was merely the opening round in what is sure to be a long, politically charged regulatory struggle.